Rubber composition for studless tires and studless tires using the same

Abstract

On icy and snowy roads, the coefficient of friction decreases compared to ordinary roads, making them more slippery. Therefore, numerous methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. The present invention aims to provide a rubber composition for studless tires that is environmentally friendly and further enhances ice performance. [Solution] The above problem was solved by a rubber composition for studless tires containing 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polycaprolactone per 100 parts by mass of diene rubber, wherein butadiene rubber accounts for 40 parts by mass or more of the 100 parts by mass of diene rubber, and the melting point of the polycaprolactone is 30°C or higher.

Description

Technical Field

[0001] The present invention relates to a studless tire rubber composition and a studless tire using the same, and more particularly, to a studless tire rubber composition having excellent ice performance while suppressing environmental impact, and a studless tire using the same.

Background Art

[0002] On ice and snow roads, the friction coefficient is lower than on ordinary roads, making it easier to slip. Therefore, conventionally, many methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. For example, a method is known in which hard foreign substances or hollow polymers are blended into a studless compound, and by forming micro irregularities on the rubber surface, the water film generated on the surface of the ice is removed to improve the ice friction (see, for example, Patent Document 1). However, hard foreign substances and polymer compounds that have fallen off the tread surface are difficult to decompose, raising concerns about environmental problems. Therefore, at present, there is a need for a method that is environmentally friendly and further improves ice performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a studless tire rubber composition having excellent ice performance while suppressing environmental impact, and a studless tire using the same.

Means for Solving the Problems

[0005] As a result of diligent research, the inventors of the present invention have found that a rubber composition for studless tires, comprising a diene-based rubber having the measured composition, a carbon black and / or white filler, and a specific amount of polycaprolactone having specific physical properties, can solve the above problems, and thus the present invention has been completed.

[0006] In other words, the present invention provides a rubber composition for studless tires, characterized in that it contains 30 to 100 parts by mass of carbon black and / or a white filler and 1 to 30 parts by mass of polycaprolactone per 100 parts by mass of diene rubber, wherein butadiene rubber accounts for 40 parts by mass or more of the 100 parts by mass of diene rubber, and the melting point of the polycaprolactone is 30°C or higher. Furthermore, the present invention provides a studless tire in which the rubber composition for studless tires is used in the tread portion. [Effects of the Invention]

[0007] The present invention provides a rubber composition for studless tires that suppresses environmental impact and has excellent ice performance, as well as a studless tire using the same. The rubber composition for studless tires of the present invention contains specific amounts of polycaprolactone and butadiene rubber, and the hydrophilic polycaprolactone and hydrophobic butadiene rubber undergo phase separation within the composition. This creates roughness on the surface of the tire tread, improving ice performance. While complete phase separation in a composition generally raises concerns about a decrease in physical properties, the present invention specifies the amounts of polycaprolactone and butadiene rubber, thus preventing complete phase separation and suppressing a decrease in physical properties such as elongation at break. Furthermore, since polycaprolactone is biodegradable, it can reduce the environmental impact. [Brief explanation of the drawing]

[0008] [Figure 1] This is an AFM (phase image) of the rubber composition for studless tires of Example 5. [Modes for carrying out the invention]

[0009] The present invention will be described in more detail below. (Diene-based rubber) The diene rubber used in this invention can be any diene rubber that can be incorporated into a rubber composition for studless tires, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and ethylene-propylene-diene polymer (EPDM). These may be used individually or in combination of two or more. Furthermore, their molecular weight and microstructure are not particularly limited, and they may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. Furthermore, from the viewpoint of improving performance on ice, it is preferable that butadiene rubber accounts for 40 parts by mass or more, preferably 50 to 70 parts by mass, of 100 parts by mass of diene rubber. Furthermore, it is preferable that the diene-based rubber has a glass transition temperature (Tg) of -50°C or lower. By specifying the Tg in this way, the performance on ice is improved. When multiple types of diene rubber are included, the Tg as used herein is calculated based on the weighted average, which is the sum of the products obtained by multiplying the glass transition temperature of each rubber by the weight fraction of each rubber. For calculation purposes, the sum of the weight fractions of each component is assumed to be 1.0. In this invention, the glass transition temperature (Tg) refers to the temperature at the midpoint of the transition region, measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min using a thermogram. A more preferable average Tg is -100 to -50°C.

[0010] (Carbon black and / or white filler) Examples of carbon blacks used in the present invention include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF, which may be used individually or in combination of two or more. Furthermore, carbon black has a nitrogen adsorption specific surface area (N2SA) of 10-300 m², which is beneficial for improving ice performance. 2 It is preferable that the amount is / g, and 50-150m 2 It is even more preferable that it be / g. The nitrogen adsorption specific surface area (N2SA) was measured according to JIS K 6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0011] Examples of white fillers used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium dioxide, calcium sulfate, etc. These may be used individually or in combination of two or more. Of these, silica is preferred because it provides better performance on ice.

[0012] Examples of silica include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, and aluminum silicate. These may be used individually or in combination of two or more. Silica derived from biomass materials such as rice husks may also be used.

[0013] From the perspective of improving ice performance, silica has a CTAB adsorption specific surface area of ​​50-300 m². 2 It is preferable that the amount is / g, and 90-200m 2 It is even more preferable that it be / g. The CTAB adsorption specific surface area is the value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed onto the silica surface according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method".

[0014] (Polycaprolactone) The polycaprolactone used in this invention is not particularly limited as long as its melting point is 30°C or higher, but from the viewpoint of improving the effects of this invention, it is preferable that it satisfies one or more of the following conditions. (1) By selecting a polycaprolactone with a melting point of 30°C or higher as defined in the present invention, the effect of improved ice performance can be obtained, but this effect is further enhanced if the melting point is preferably 40°C or higher, and more preferably 50 to 70°C. (2) The melt flow rate of polycaprolactone measured at 160°C and a load of 2.16 kg is preferably 200 g / 10 min or less, and more preferably 1 to 100 g / 10 min. By setting the melt flow rate within the above range, phase separation of polycaprolactone and butadiene rubber occurs within a range that does not impair the physical properties, and the ice performance is improved. In the following description, the melt flow rate of polycaprolactone is the value measured under the above conditions. (3) The number average molecular weight of the polycaprolactone is preferably 30,000 or more, more preferably 35,000 to 120,000. By setting the number average molecular weight within the above range, phase separation between the polycaprolactone and the butadiene rubber occurs within a range that does not impair the physical properties, and the performance on ice is improved. The melting point is measured by differential scanning calorimetry (DSC) in accordance with ASTM D3418 at a heating rate of 10 °C / min, the melt mass flow rate (MFR) is measured in accordance with JIS K7210:1999, and the number average molecular weight is measured as a polystyrene equivalent value using GPC.

[0015] (Blending ratio of the studless tire rubber composition) The rubber composition for studless tires of the present invention contains 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polycaprolactone with respect to 100 parts by mass of the diene rubber, and 40 parts by mass or more of butadiene rubber occupies in 100 parts by mass of the diene rubber. When the blending amount of the carbon black and / or white filler is less than 30 parts by mass with respect to 100 parts by mass of the diene rubber, the mechanical properties and abrasion resistance of the rubber composition for studless tires deteriorate. On the contrary, when it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition for studless tires decreases and the performance on ice deteriorates. When the blending amount of the polycaprolactone is less than 1 part by mass with respect to 100 parts by mass of the diene rubber, the addition amount is too small to exhibit the effects of the present invention. On the contrary, when it exceeds 30 parts by mass, the degree of improvement in the performance on ice is poor. [[ID=​​​​​​​​​​​ In addition to the components mentioned above, the rubber composition for studless tires in the present invention may contain various additives commonly used in rubber compositions for studless tires, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; antioxidants; plasticizers; silane coupling agents; and thermally expandable microcapsules. These additives can be mixed in a conventional manner to form a composition, which can then be used for vulcanization or crosslinking. The amounts of these additives can also be the conventional amounts, as long as they do not contradict the objectives of the present invention.

[0018] Furthermore, the tire of the present invention can be prepared using the rubber composition for studless tires of the present invention, and is preferably a pneumatic tire, which can be filled with air, nitrogen or other inert gases and other gases. The tire of the present invention is also preferably applied to the tread portion, especially the cap tread portion, to form a studless tire. [Examples]

[0019] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0020] Standard Example 1, Examples 1-5, Comparative Examples 1-2 In the formulations (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) and curing agent were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. Subsequently, the composition was put back into the same Banbury mixer, the vulcanization system was added and kneaded to obtain a rubber composition for studless tires.

[0021] Elongation at Break: The obtained rubber composition for studless tires was vulcanized at 170°C for 10 minutes using a mold of a predetermined shape (internal dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare vulcanized rubber test specimens. Using these vulcanized rubber test specimens, dumbbell-type JIS No. 3 test specimens were prepared in accordance with JIS K6251, and tensile tests were performed at room temperature (20°C) at a tensile speed of 500 mm / min to measure the tensile elongation at break. The obtained results are shown as an index with the value of Standard Example 1 set to 100. A larger index indicates a larger tensile elongation at break. An index of 106 or higher is preferable. Ice Performance: The obtained studless tire rubber composition was used for the tread portion, vulcanized, and molded to produce a pneumatic tire (tire size: 215 / 60R16). The above pneumatic tire was mounted on a 16×7J rim, inflated to 220 [kPa] air pressure, and mounted on a test vehicle (Japanese 2-liter sedan FF vehicle). Subsequently, the test vehicle was subjected to emergency braking from an initial speed of 40 [km / h] on an icy test course, and the braking distance until a complete stop was measured. The braking distance results measured as described above are shown as an index with the reciprocal of Standard Example 1 set to 100. A larger index indicates better ice performance.

[0022] The results are shown in Table 1.

[0023] [Table 1]

[0024] *1: NR (STR20 manufactured by Bombandit, glass transition temperature = -65°C) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = -110℃) *3: Silica (ULTRASIL VN3 manufactured by Evonik DeGussa) *4: Carbon black (Show Black N339 manufactured by Cabot Japan Co., Ltd.) *5: Silane coupling agent (Si69 manufactured by Evonik DeGussa) *6: Zinc oxide (3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd.) *7: Stearic acid (YR bead stearic acid manufactured by NOF Corporation) *8: Anti-aging agent (Santoflex 6PPD manufactured by Flexis, an amine-based anti-aging agent) *9: Wax (Paraffin wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *10: Oil (Shell Lubricants Japan Extract No. 4S, aroma oil) *11: Sulfur (5% oil-treated sulfur manufactured by Hosoi Chemical Industry Co., Ltd.) *12: Vulcanization accelerator (Sunceller CM-G, manufactured by Sanshin Chemical Industry Co., Ltd.) *13: Polycaprolactone 1 (Capa 6250, manufactured by Ingevity (melting point: 58-60°C, number average molecular weight: 25,000, melt flow rate: 250g / 10min)) *14: Polycaprolactone 2 (Capa 6400, manufactured by Ingevity (melting point: 58-60℃, number average molecular weight: 37,000, melt flow rate: 75g / 10min)) *15: Polycaprolactone 3 (Capa 6500, manufactured by Ingevity (melting point: 58-60℃, number average molecular weight: 50,000, melt flow rate: 18g / 10min)) *16: Polycaprolactone 4 (Capa 6800, manufactured by Ingevity (melting point: 58-60℃, number average molecular weight: 80,000, melt flow rate: 2.4g / 10min)) *17: Polycaprolactone 5 (Capa 2043, manufactured by Ingevity, Inc. (melting point: 0-18℃, number average molecular weight: 400))

[0025] As shown in Table 1, the studless tire rubber compositions of each example contain 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polycaprolactone per 100 parts by mass of diene rubber, with butadiene rubber accounting for 40 parts by mass or more of the 100 parts by mass of diene rubber, and the melting point of the polycaprolactone being 30°C or higher. As a result, the ice performance and elongation at break are improved compared to Standard Example 1. On the other hand, Comparative Example 1 did not show as much improvement in ice performance and elongation at break as the Examples because the amount of polycaprolactone used exceeded the upper limit specified in the present invention. Comparative Example 2 did not show any improvement in ice performance or elongation at break because the melting point of polycaprolactone was less than 30°C. Figure 1 shows an AFM (phase image) of the studless tire rubber composition of Example 5. The black areas are thought to be silica and carbon black, the light gray areas are thought to be the rubber portion, and the dark gray area in the middle is thought to be polycaprolactone.

[0026] Standard Example 2 and Comparative Example 3 In the aforementioned "Standard Example 1, Examples 1-5, and Comparative Examples 1-2," the process was repeated except for changing the formulation of each raw material as shown in Table 2 below. Comparative Example 3 was compared with Standard Example 2. The results are shown in Table 2.

[0027] [Table 2]

[0028] Standard Example 2 and Comparative Example 3 in Table 2 are examples in which 100% natural rubber was used as the diene rubber. Referring to the results of Comparative Example 3, although polycaprolactone 2, which is within the scope of the present invention, was used, but butadiene rubber was not used as the diene rubber, so no improvement in ice performance or elongation at break was observed.

[0029] The present invention encompasses the following embodiments. Embodiment 1: The material contains 30 to 100 parts by mass of carbon black and / or white filler, and 1 to 30 parts by mass of polycaprolactone per 100 parts by mass of diene rubber. Of the 100 parts by mass of the diene rubber, butadiene rubber accounts for 40 parts by mass or more, and The melting point of the polycaprolactone is 30°C or higher. A rubber composition for studless tires characterized by the following features. Embodiment 2: The rubber composition for studless tires according to Embodiment 1, characterized in that it contains 10 to 100 parts by mass of silica as a white filler per 100 parts by mass of the diene rubber. Embodiment 3: The rubber composition for studless tires according to Embodiment 1 or 2, characterized in that the melt flow rate of the polycaprolactone measured under conditions of 160°C and a load of 2.16 kg is 200 g / 10 min or less. Embodiment 4: The rubber composition for studless tires according to any one of Embodiments 1 to 3, characterized in that the number average molecular weight of the polycaprolactone is 30,000 or more. Embodiment 5: A rubber composition for studless tires according to any one of Embodiments 1 to 4, characterized in that the average glass transition temperature of the diene rubber is -100 to -50°C. Embodiment 6: A studless tire using the studless tire rubber composition described in any of Embodiments 1 to 5 in the tread portion.

Claims

1. The material contains 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polycaprolactone per 100 parts by mass of diene rubber. Of the 100 parts by mass of the diene rubber, butadiene rubber accounts for 40 parts by mass or more, and The melting point of the polycaprolactone is 30°C or higher. A rubber composition for studless tires characterized by the following features.

2. The rubber composition for studless tires according to claim 1, characterized in that it contains 10 to 100 parts by mass of silica as a white filler per 100 parts by mass of the diene rubber.

3. The rubber composition for studless tires according to claim 1, characterized in that the melt flow rate of the polycaprolactone measured under conditions of 160°C and a load of 2.16 kg is 200 g / 10 min or less.

4. The rubber composition for studless tires according to claim 1, characterized in that the number average molecular weight of the polycaprolactone is 30,000 or more.

5. The rubber composition for studless tires according to claim 1, characterized in that the average glass transition temperature of the diene rubber is -100 to -50°C.

6. A studless tire using the studless tire rubber composition described in claim 1 in the tread portion.

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